/*
   * User-space I/O driver support for HID subsystem
   * Copyright (c) 2012 David Herrmann
   */
  
  /*
   * This program is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License as published by the Free
   * Software Foundation; either version 2 of the License, or (at your option)
   * any later version.
   */
  
  #include <linux/atomic.h>
  #include <linux/compat.h>
  #include <linux/device.h>
  #include <linux/fs.h>
  #include <linux/hid.h>
  #include <linux/input.h>
  #include <linux/miscdevice.h>
  #include <linux/module.h>
  #include <linux/mutex.h>
  #include <linux/poll.h>
  #include <linux/sched.h>
  #include <linux/spinlock.h>
  #include <linux/uhid.h>
  #include <linux/wait.h>
  
  #define UHID_NAME	"uhid"
  #define UHID_BUFSIZE	32
  
  struct uhid_device {
  	struct mutex devlock;
  	bool running;
  
  	__u8 *rd_data;
  	uint rd_size;
  
  	struct hid_device *hid;
  	struct uhid_event input_buf;
  
  	wait_queue_head_t waitq;
  	spinlock_t qlock;
  	__u8 head;
  	__u8 tail;
  	struct uhid_event *outq[UHID_BUFSIZE];
  
  	struct mutex report_lock;
  	wait_queue_head_t report_wait;
  	atomic_t report_done;
  	atomic_t report_id;
  	struct uhid_event report_buf;
  };
  
  static struct miscdevice uhid_misc;
  
  static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
  {
  	__u8 newhead;
  
  	newhead = (uhid->head + 1) % UHID_BUFSIZE;
  
  	if (newhead != uhid->tail) {
  		uhid->outq[uhid->head] = ev;
  		uhid->head = newhead;
  		wake_up_interruptible(&uhid->waitq);
  	} else {
  		hid_warn(uhid->hid, "Output queue is full
  ");
  		kfree(ev);
  	}
  }
  
  static int uhid_queue_event(struct uhid_device *uhid, __u32 event)
  {
  	unsigned long flags;
  	struct uhid_event *ev;
  
  	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
  	if (!ev)
  		return -ENOMEM;
  
  	ev->type = event;
  
  	spin_lock_irqsave(&uhid->qlock, flags);
  	uhid_queue(uhid, ev);
  	spin_unlock_irqrestore(&uhid->qlock, flags);
  
  	return 0;
  }
  
  static int uhid_hid_start(struct hid_device *hid)
  {
  	struct uhid_device *uhid = hid->driver_data;
  
  	return uhid_queue_event(uhid, UHID_START);
  }
  
  static void uhid_hid_stop(struct hid_device *hid)
  {
  	struct uhid_device *uhid = hid->driver_data;
  
  	hid->claimed = 0;
  	uhid_queue_event(uhid, UHID_STOP);
  }
  
  static int uhid_hid_open(struct hid_device *hid)
  {
  	struct uhid_device *uhid = hid->driver_data;
  
  	return uhid_queue_event(uhid, UHID_OPEN);
  }
  
  static void uhid_hid_close(struct hid_device *hid)
  {
  	struct uhid_device *uhid = hid->driver_data;
  
  	uhid_queue_event(uhid, UHID_CLOSE);
  }
  
  static int uhid_hid_parse(struct hid_device *hid)
  {
  	struct uhid_device *uhid = hid->driver_data;
  
  	return hid_parse_report(hid, uhid->rd_data, uhid->rd_size);
  }
  
  static int uhid_hid_get_raw(struct hid_device *hid, unsigned char rnum,
  			    __u8 *buf, size_t count, unsigned char rtype)
  {
  	struct uhid_device *uhid = hid->driver_data;
  	__u8 report_type;
  	struct uhid_event *ev;
  	unsigned long flags;
  	int ret;
  	size_t uninitialized_var(len);
  	struct uhid_feature_answer_req *req;
  
  	if (!uhid->running)
  		return -EIO;
  
  	switch (rtype) {
  	case HID_FEATURE_REPORT:
  		report_type = UHID_FEATURE_REPORT;
  		break;
  	case HID_OUTPUT_REPORT:
  		report_type = UHID_OUTPUT_REPORT;
  		break;
  	case HID_INPUT_REPORT:
  		report_type = UHID_INPUT_REPORT;
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	ret = mutex_lock_interruptible(&uhid->report_lock);
  	if (ret)
  		return ret;
  
  	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
  	if (!ev) {
  		ret = -ENOMEM;
  		goto unlock;
  	}
  
  	spin_lock_irqsave(&uhid->qlock, flags);
  	ev->type = UHID_FEATURE;
  	ev->u.feature.id = atomic_inc_return(&uhid->report_id);
  	ev->u.feature.rnum = rnum;
  	ev->u.feature.rtype = report_type;
  
  	atomic_set(&uhid->report_done, 0);
  	uhid_queue(uhid, ev);
  	spin_unlock_irqrestore(&uhid->qlock, flags);
  
  	ret = wait_event_interruptible_timeout(uhid->report_wait,
  				atomic_read(&uhid->report_done), 5 * HZ);
  
  	/*
  	 * Make sure "uhid->running" is cleared on shutdown before
  	 * "uhid->report_done" is set.
  	 */
  	smp_rmb();
  	if (!ret || !uhid->running) {
  		ret = -EIO;
  	} else if (ret < 0) {
  		ret = -ERESTARTSYS;
  	} else {
  		spin_lock_irqsave(&uhid->qlock, flags);
  		req = &uhid->report_buf.u.feature_answer;
  
  		if (req->err) {
  			ret = -EIO;
  		} else {
  			ret = 0;
  			len = min(count,
  				min_t(size_t, req->size, UHID_DATA_MAX));
  			memcpy(buf, req->data, len);
  		}
  
  		spin_unlock_irqrestore(&uhid->qlock, flags);
  	}
  
  	atomic_set(&uhid->report_done, 1);
  
  unlock:
  	mutex_unlock(&uhid->report_lock);
  	return ret ? ret : len;
  }
  
  static int uhid_hid_output_raw(struct hid_device *hid, __u8 *buf, size_t count,
  			       unsigned char report_type)
  {
  	struct uhid_device *uhid = hid->driver_data;
  	__u8 rtype;
  	unsigned long flags;
  	struct uhid_event *ev;
  
  	switch (report_type) {
  	case HID_FEATURE_REPORT:
  		rtype = UHID_FEATURE_REPORT;
  		break;
  	case HID_OUTPUT_REPORT:
  		rtype = UHID_OUTPUT_REPORT;
  		break;
  	default:
  		return -EINVAL;
  	}
  
  	if (count < 1 || count > UHID_DATA_MAX)
  		return -EINVAL;
  
  	ev = kzalloc(sizeof(*ev), GFP_KERNEL);
  	if (!ev)
  		return -ENOMEM;
  
  	ev->type = UHID_OUTPUT;
  	ev->u.output.size = count;
  	ev->u.output.rtype = rtype;
  	memcpy(ev->u.output.data, buf, count);
  
  	spin_lock_irqsave(&uhid->qlock, flags);
  	uhid_queue(uhid, ev);
  	spin_unlock_irqrestore(&uhid->qlock, flags);
  
  	return count;
  }
  
  static struct hid_ll_driver uhid_hid_driver = {
  	.start = uhid_hid_start,
  	.stop = uhid_hid_stop,
  	.open = uhid_hid_open,
  	.close = uhid_hid_close,
  	.parse = uhid_hid_parse,
  };
  
  #ifdef CONFIG_COMPAT
  
  /* Apparently we haven't stepped on these rakes enough times yet. */
  struct uhid_create_req_compat {
  	__u8 name[128];
  	__u8 phys[64];
  	__u8 uniq[64];
  
  	compat_uptr_t rd_data;
  	__u16 rd_size;
  
  	__u16 bus;
  	__u32 vendor;
  	__u32 product;
  	__u32 version;
  	__u32 country;
  } __attribute__((__packed__));
  
  static int uhid_event_from_user(const char __user *buffer, size_t len,
  				struct uhid_event *event)
  {
  	if (is_compat_task()) {
  		u32 type;
  
  		if (get_user(type, buffer))
  			return -EFAULT;
  
  		if (type == UHID_CREATE) {
  			/*
  			 * This is our messed up request with compat pointer.
  			 * It is largish (more than 256 bytes) so we better
  			 * allocate it from the heap.
  			 */
  			struct uhid_create_req_compat *compat;
  
  			compat = kzalloc(sizeof(*compat), GFP_KERNEL);
  			if (!compat)
  				return -ENOMEM;
  
  			buffer += sizeof(type);
  			len -= sizeof(type);
  			if (copy_from_user(compat, buffer,
  					   min(len, sizeof(*compat)))) {
  				kfree(compat);
  				return -EFAULT;
  			}
  
  			/* Shuffle the data over to proper structure */
  			event->type = type;
  
  			memcpy(event->u.create.name, compat->name,
  				sizeof(compat->name));
  			memcpy(event->u.create.phys, compat->phys,
  				sizeof(compat->phys));
  			memcpy(event->u.create.uniq, compat->uniq,
  				sizeof(compat->uniq));
  
  			event->u.create.rd_data = compat_ptr(compat->rd_data);
  			event->u.create.rd_size = compat->rd_size;
  
  			event->u.create.bus = compat->bus;
  			event->u.create.vendor = compat->vendor;
  			event->u.create.product = compat->product;
  			event->u.create.version = compat->version;
  			event->u.create.country = compat->country;
  
  			kfree(compat);
  			return 0;
  		}
  		/* All others can be copied directly */
  	}
  
  	if (copy_from_user(event, buffer, min(len, sizeof(*event))))
  		return -EFAULT;
  
  	return 0;
  }
  #else
  static int uhid_event_from_user(const char __user *buffer, size_t len,
  				struct uhid_event *event)
  {
  	if (copy_from_user(event, buffer, min(len, sizeof(*event))))
  		return -EFAULT;
  
  	return 0;
  }
  #endif
  
  static int uhid_dev_create(struct uhid_device *uhid,
  			   const struct uhid_event *ev)
  {
  	struct hid_device *hid;
  	int ret;
  
  	if (uhid->running)
  		return -EALREADY;
  
  	uhid->rd_size = ev->u.create.rd_size;
  	if (uhid->rd_size <= 0 || uhid->rd_size > HID_MAX_DESCRIPTOR_SIZE)
  		return -EINVAL;
  
  	uhid->rd_data = kmalloc(uhid->rd_size, GFP_KERNEL);
  	if (!uhid->rd_data)
  		return -ENOMEM;
  
  	if (copy_from_user(uhid->rd_data, ev->u.create.rd_data,
  			   uhid->rd_size)) {
  		ret = -EFAULT;
  		goto err_free;
  	}
  
  	hid = hid_allocate_device();
  	if (IS_ERR(hid)) {
  		ret = PTR_ERR(hid);
  		goto err_free;
  	}
  
  	strncpy(hid->name, ev->u.create.name, 127);
  	hid->name[127] = 0;
  	strncpy(hid->phys, ev->u.create.phys, 63);
  	hid->phys[63] = 0;
  	strncpy(hid->uniq, ev->u.create.uniq, 63);
  	hid->uniq[63] = 0;
  
  	hid->ll_driver = &uhid_hid_driver;
  	hid->hid_get_raw_report = uhid_hid_get_raw;
  	hid->hid_output_raw_report = uhid_hid_output_raw;
  	hid->bus = ev->u.create.bus;
  	hid->vendor = ev->u.create.vendor;
  	hid->product = ev->u.create.product;
  	hid->version = ev->u.create.version;
  	hid->country = ev->u.create.country;
  	hid->driver_data = uhid;
  	hid->dev.parent = uhid_misc.this_device;
  
  	uhid->hid = hid;
  	uhid->running = true;
  
  	ret = hid_add_device(hid);
  	if (ret) {
  		hid_err(hid, "Cannot register HID device
  ");
  		goto err_hid;
  	}
  
  	return 0;
  
  err_hid:
  	hid_destroy_device(hid);
  	uhid->hid = NULL;
  	uhid->running = false;
  err_free:
  	kfree(uhid->rd_data);
  	return ret;
  }
  
  static int uhid_dev_destroy(struct uhid_device *uhid)
  {
  	if (!uhid->running)
  		return -EINVAL;
  
  	/* clear "running" before setting "report_done" */
  	uhid->running = false;
  	smp_wmb();
  	atomic_set(&uhid->report_done, 1);
  	wake_up_interruptible(&uhid->report_wait);
  
  	hid_destroy_device(uhid->hid);
  	kfree(uhid->rd_data);
  
  	return 0;
  }
  
  static int uhid_dev_input(struct uhid_device *uhid, struct uhid_event *ev)
  {
  	if (!uhid->running)
  		return -EINVAL;
  
  	hid_input_report(uhid->hid, HID_INPUT_REPORT, ev->u.input.data,
  			 min_t(size_t, ev->u.input.size, UHID_DATA_MAX), 0);
  
  	return 0;
  }
  
  static int uhid_dev_feature_answer(struct uhid_device *uhid,
  				   struct uhid_event *ev)
  {
  	unsigned long flags;
  
  	if (!uhid->running)
  		return -EINVAL;
  
  	spin_lock_irqsave(&uhid->qlock, flags);
  
  	/* id for old report; drop it silently */
  	if (atomic_read(&uhid->report_id) != ev->u.feature_answer.id)
  		goto unlock;
  	if (atomic_read(&uhid->report_done))
  		goto unlock;
  
  	memcpy(&uhid->report_buf, ev, sizeof(*ev));
  	atomic_set(&uhid->report_done, 1);
  	wake_up_interruptible(&uhid->report_wait);
  
  unlock:
  	spin_unlock_irqrestore(&uhid->qlock, flags);
  	return 0;
  }
  
  static int uhid_char_open(struct inode *inode, struct file *file)
  {
  	struct uhid_device *uhid;
  
  	uhid = kzalloc(sizeof(*uhid), GFP_KERNEL);
  	if (!uhid)
  		return -ENOMEM;
  
  	mutex_init(&uhid->devlock);
  	mutex_init(&uhid->report_lock);
  	spin_lock_init(&uhid->qlock);
  	init_waitqueue_head(&uhid->waitq);
  	init_waitqueue_head(&uhid->report_wait);
  	uhid->running = false;
  	atomic_set(&uhid->report_done, 1);
  
  	file->private_data = uhid;
  	nonseekable_open(inode, file);
  
  	return 0;
  }
  
  static int uhid_char_release(struct inode *inode, struct file *file)
  {
  	struct uhid_device *uhid = file->private_data;
  	unsigned int i;
  
  	uhid_dev_destroy(uhid);
  
  	for (i = 0; i < UHID_BUFSIZE; ++i)
  		kfree(uhid->outq[i]);
  
  	kfree(uhid);
  
  	return 0;
  }
  
  static ssize_t uhid_char_read(struct file *file, char __user *buffer,
  				size_t count, loff_t *ppos)
  {
  	struct uhid_device *uhid = file->private_data;
  	int ret;
  	unsigned long flags;
  	size_t len;
  
  	/* they need at least the "type" member of uhid_event */
  	if (count < sizeof(__u32))
  		return -EINVAL;
  
  try_again:
  	if (file->f_flags & O_NONBLOCK) {
  		if (uhid->head == uhid->tail)
  			return -EAGAIN;
  	} else {
  		ret = wait_event_interruptible(uhid->waitq,
  						uhid->head != uhid->tail);
  		if (ret)
  			return ret;
  	}
  
  	ret = mutex_lock_interruptible(&uhid->devlock);
  	if (ret)
  		return ret;
  
  	if (uhid->head == uhid->tail) {
  		mutex_unlock(&uhid->devlock);
  		goto try_again;
  	} else {
  		len = min(count, sizeof(**uhid->outq));
  		if (copy_to_user(buffer, uhid->outq[uhid->tail], len)) {
  			ret = -EFAULT;
  		} else {
  			kfree(uhid->outq[uhid->tail]);
  			uhid->outq[uhid->tail] = NULL;
  
  			spin_lock_irqsave(&uhid->qlock, flags);
  			uhid->tail = (uhid->tail + 1) % UHID_BUFSIZE;
  			spin_unlock_irqrestore(&uhid->qlock, flags);
  		}
  	}
  
  	mutex_unlock(&uhid->devlock);
  	return ret ? ret : len;
  }
  
  static ssize_t uhid_char_write(struct file *file, const char __user *buffer,
  				size_t count, loff_t *ppos)
  {
  	struct uhid_device *uhid = file->private_data;
  	int ret;
  	size_t len;
  
  	/* we need at least the "type" member of uhid_event */
  	if (count < sizeof(__u32))
  		return -EINVAL;
  
  	ret = mutex_lock_interruptible(&uhid->devlock);
  	if (ret)
  		return ret;
  
  	memset(&uhid->input_buf, 0, sizeof(uhid->input_buf));
  	len = min(count, sizeof(uhid->input_buf));
  
  	ret = uhid_event_from_user(buffer, len, &uhid->input_buf);
  	if (ret)
  		goto unlock;
  
  	switch (uhid->input_buf.type) {
  	case UHID_CREATE:
  		ret = uhid_dev_create(uhid, &uhid->input_buf);
  		break;
  	case UHID_DESTROY:
  		ret = uhid_dev_destroy(uhid);
  		break;
  	case UHID_INPUT:
  		ret = uhid_dev_input(uhid, &uhid->input_buf);
  		break;
  	case UHID_FEATURE_ANSWER:
  		ret = uhid_dev_feature_answer(uhid, &uhid->input_buf);
  		break;
  	default:
  		ret = -EOPNOTSUPP;
  	}
  
  unlock:
  	mutex_unlock(&uhid->devlock);
  
  	/* return "count" not "len" to not confuse the caller */
  	return ret ? ret : count;
  }
  
  static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
  {
  	struct uhid_device *uhid = file->private_data;
  
  	poll_wait(file, &uhid->waitq, wait);
  
  	if (uhid->head != uhid->tail)
  		return POLLIN | POLLRDNORM;
  
  	return 0;
  }
  
  static const struct file_operations uhid_fops = {
  	.owner		= THIS_MODULE,
  	.open		= uhid_char_open,
  	.release	= uhid_char_release,
  	.read		= uhid_char_read,
  	.write		= uhid_char_write,
  	.poll		= uhid_char_poll,
  	.llseek		= no_llseek,
  };
  
  static struct miscdevice uhid_misc = {
  	.fops		= &uhid_fops,
  	.minor		= UHID_MINOR,
  	.name		= UHID_NAME,
  };
  
  static int __init uhid_init(void)
  {
  	return misc_register(&uhid_misc);
  }
  
  static void __exit uhid_exit(void)
  {
  	misc_deregister(&uhid_misc);
  }
  
  module_init(uhid_init);
  module_exit(uhid_exit);
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("David Herrmann <dh.herrmann@gmail.com>");
  MODULE_DESCRIPTION("User-space I/O driver support for HID subsystem");
  MODULE_ALIAS_MISCDEV(UHID_MINOR);
  MODULE_ALIAS("devname:" UHID_NAME);